Master Operational Technology Communication Protocol
Modbus TCP/IP is an industrial communication protocol that enables automation devices to exchange data over TCP/IP networks. Developed in 1979 by Modicon (now Schneider Electric), it has become the de facto standard for industrial automation communications.
Read/Write single bits (digital outputs)
Example: Motor start/stop commands
Read-only single bits (digital inputs)
Example: Sensor status, limit switches
Read-only 16-bit values (analog inputs)
Example: Temperature, pressure readings
Read/Write 16-bit values (analog outputs)
Example: Setpoints, configuration values
1. Client sends request → 2. Server processes → 3. Server sends response
The Modbus Application Protocol (MBAP) header is 7 bytes long and precedes every Modbus TCP message.
This header would be followed by the Function Code and Data fields
Allows client to match responses with requests. Critical for networks with multiple simultaneous transactions.
Identifies the protocol being used. Always 0x0000 for standard Modbus operations.
Specifies the number of bytes that follow this field, including Unit ID, Function Code, and Data.
Identifies the target device. Useful for Modbus gateways that bridge to serial devices.
Purpose: Read 1-2000 coil status
Use Case: Check motor running status, valve positions
Purpose: Read 1-125 holding registers
Use Case: Read setpoints, process values
Purpose: Write value to one register
Use Case: Set temperature setpoint, speed reference
Purpose: Write values to multiple registers
Use Case: Configure multiple parameters at once
Scenario: Monitoring electrical consumption across a manufacturing facility
Setup: Power meters with Modbus TCP → Ethernet network → SCADA system
Data Exchanged: Voltage, current, power consumption, energy totals
Benefits: Real-time monitoring, automated reporting, predictive maintenance
Scenario: HVAC control in a commercial building
Setup: Temperature controllers, damper actuators → Building management system
Data Exchanged: Temperature readings, setpoints, equipment status
Benefits: Energy efficiency, comfort control, maintenance scheduling
Scenario: Controlling pumps, valves, and monitoring water quality
Setup: PLCs controlling field devices → Central SCADA system
Data Exchanged: Flow rates, pressure, pH levels, pump status
Benefits: Process optimization, regulatory compliance, remote operation
Scenario: Coordinating conveyor systems and assembly stations
Setup: Multiple PLCs → HMI stations → MES (Manufacturing Execution System)
Data Exchanged: Production counts, quality data, equipment status
Benefits: Production tracking, quality control, efficiency optimization